This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled SHADING CORRECTION METHOD ON SHUTTLE SCANNING DEVICE filed with the Korean Industrial Property Office on Nov. 29, 1997 and there duly assigned Serial No. 64363/1997 by that Office.
1. Field of the Invention
The present invention relates to a method for optical scanning, and more particularly to a method for providing a shading correction for a reciprocating, shuttle scanner.
2. Discussion of Related Art
A shading correction method used in a conventional shuttle scanning device involves reading a value with the scan head in a stopped state after the scan head is moved to a position on a reference white panel. The shading correction method involves using this value at the time of an actual scanning of a document by employing the value as a shading factor, after having scanned through throwing lights at a position located by the white panel.
In the case of a particular method, median filtering is used in order to avoid a shading correction error which can occur through reading a polluted or dirty part of the white panel. This is a method of eliminating spot noises by excluding a maximal value and a minimal value. Further, a method of using an average value, taken after having read the white panel several times, as a factor value is also used to avoid a line movement after a shading correction due to nonuniformity of the shading factor due to white, Gaussian, random noise.
The shuttle scanner operates scanning at a right angle to the feeding direction. When scanning, the scan head is not in an ideal stopped state and so inclination occurs. For this reason, a difference can occur between the scanning state at the time of the reading to determine the shading factor and the scanning state at the time of scanning an actual image area. As a result of this inaccuracy of the shading correction, more errors may occur than in case of not taking an average value.
The shading correction method using the shading factor average value involves taking an average value by reading the shading factor several times with the scan head in a stopped position. Accordingly, this method has a disadvantage of insufficiently reproducing the shading situation when the scan head is actually moving.
Based on my observation of the art, I have found that what is needed is a method of providing a shading correction which avoids the errors associated with the methods of the background art. In particular, I wish to eliminate the problems associated with using a shading factor obtained using a stopped print head for scans obtained using a moving scan head.
It is therefore an object of the present invention to provide an improved method for performing a shading correction for a shuttle scanner.
It is a further object to provide a method for providing a precise scanning reference value for use in a shading correction.
It is a yet further object to provide a method for performing a shading correction which prevents incorrect measurement of the shading correction factor.
It is a still further object to provide a method for performing a shading correction which avoids the inaccuracy due to measuring the shading correction factor while the scan head is stopped.
It is a still yet further object to provide a method for performing a shading correction which avoids errors due to dirt on the reference white panel.
It is another object of the present invention to provide a shading correction under condition similar to an actual scanning operation by measuring the shading factor while the scan head is moving.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a method of calculating a precise scanning reference value for a shading correction by dividing a scanning area under a reciprocating scan head into a practical scanning area and a shading correction scanning area. This method includes the steps of: entering a shading correction mode; moving the scanner to the shading correction scanning area; reading a plural number of scanning values while moving within the shading correction scanning area; and determining the scanning reference value by using said plural number of scanning values.